(1) Field of the Invention
The present invention relates to a display device for use in a vehicle and, more specifically, to a display device for use in a vehicle, by which an image for superposition displayed on a display source is projected on a windshield of the vehicle so that a driver can see the foreground of the vehicle visible through the windshield together with a virtual image of the image for superposition, which is superposed upon the foreground.
(2) Description of the Related Art
Recently, with increase and diversification of information required by a driver during a drive, a projection-type display unit called a head up display has been adopted so that information, which cannot be displayed in a meter unit due to the lack of the space, is displayed on a windshield as a virtual image, thereby a driver can see the foreground of the vehicle through the windshield together with the virtual image, which is superposed upon the foreground.
In such a projection-type display unit, since a windshield on which an image from an image source is projected has not a plane surface, and the curvature and the angle of inclination relatively to the horizontal plane (or vertical plane) are different depending upon the position on the windshield, therefore the virtual image projected on the windshield is distorted, thereby affecting the visibility of the virtual image.
In order to solve the problem described above, the correction of distortion of the virtual image projected on a windshield has been proposed by using an optical element or by controlling the display as disclosed, for example, in Japanese Patent Application Laid-Open No. H3-113413 and No. H4-283790.
However, these proposals do not take the following situation into consideration: that is, a seat position and a physique of a driver change depending upon the driver, resulting in that a position on the windshield to be seen from the eye point cannot be determined at a specific position; and the contents or degree of distortion of a virtual image to be seen on the windshield changes depending upon a shape of the windshield, which may change depending upon the type of the vehicle. Therefore, a correction of the distortion is carried out uniformly, thereby being unable to respond to the situations described above.
It is therefore an objective of the present invention to solve the above problem and to provide a display device for use in a vehicle, by which an image for superposition displayed on a display source is projected on a non-plane windshield of the vehicle so that the foreground of the vehicle visible through the windshield and a virtual image of the image for superposition projected on the windshield, which is superposed upon the foreground, are seen together, and by which the distortion of a virtual image on the windshield can adequately be canceled: even when a seat position and a physique of a driver change depending upon the driver, resulting in that a position on the windshield to be seen from the eye point cannot be determined at a specific position; and when the contents or degree of distortion of a virtual image to be seen on the windshield changes depending upon a shape of the windshield, which may change depending upon the type of.the vehicle.
In order to attain the above objective, the present invention is to provide a display device for use in a vehicle, by which an image for superposition displayed on a display source is projected on a windshield of the vehicle so that the foreground of the vehicle visible from an eye point of the vehicle through the windshield and a virtual image of the image for superposition projected on the windshield, which is superposed upon the foreground, are seen together, comprising:
image distortion generating means for distorting the image for superposition in advance and displaying the distorted image for superposition on the display source so that distortion arisen in the virtual image of the image for superposition to be seen from the eye point due to non-flatness of the windshield is canceled out; and
distortion pattern adjusting means for adjusting the amount of the distortion of the image for superposition displayed on the display source generated by the image distortion generating means with respect to upper and lower directions and right and left directions of the vehicle in the virtual image of the image for superposition,
wherein the distortion pattern adjusting means adjusts a distortion pattern of the image for superposition displayed on the display source generated by the image distortion generating means to a distortion pattern in response to the non-flatness of the windshield and a positional relationship between the windshield and the eye point.
With the construction described above, the distortion of the virtual image of the image for superposition projected on the windshield can adequately be canceled out.
Preferably, the image distortion generating means displays a distorted lattice image for adjustment, in which a lattice image consisting of straight lines is distorted, on the display source as the image for superposition when the distortion pattern adjusting means adjusts a distortion pattern of the image for superposition displayed on the display source generated by the image distortion generating means.
With the construction described above, the distortion pattern generated by the image distortion generating means can easily be adjusted to a pattern, which precisely cancels out the distortion arisen in the virtual image of the image for superposition seen from the eye point due to the non-flatness of the windshield.
Preferably, the image distortion generating means comprises:
holding means for holding a coordinate conversion table indicating a correspondence between each pixel of an image signal of the image for superposition and each pixel of an image signal of the distorted image for superposition, in which the image for superposition being distorted in advance and displayed on the display source; and
signal generating means for generating an image signal of the distorted image for superposition, by assigning data for each pixel of an image signal of the image for superposition as data for corresponding each pixel in the image signal of the distorted image for superposition, on the basis of the coordinate conversion table,
wherein the distortion pattern adjusting means adjusts a distortion pattern of the image for superposition displayed on the display source generated by the image distortion generating means at least in response to a change in contents of the coordinate conversion table.
With the construction described above, the distortion of the virtual image of the image for superposition projected on the windshield can adequately be canceled out.
Preferably, the holding means consists of a replaceable storage medium, which constitutes the distortion pattern adjusting means.
With the construction described above, the distortion of the virtual image of the image for superposition projected on the windshield can adequately be canceled out only by replacing a storage medium, which constitutes the holding means.